[科学60秒] 地球诞生之初的岩石
参考文本：
The Earth’s crust is old. Billions of years old. So old that it’s nearly impossible to imagine. And now scientists have discovered what may be the oldest whole rocks ever known. Geologists at Carnegie Mellon University published the results of the research in the September 26th issue of the journal Science.
The rocks come from an area of the Hudson Bay in northern Quebec. In 2001 the geologists identified the site as a possible repository of very old rocks. It is made up of folds of volcanic and what are called metasedentary rocks. And it’s surrounded by three-and-a-half-billion-year-old tonalite.
Researchers collected rocks and measured minute isotopic variations in rare earth elements called neodymium and samarium. According to dating techniques, the rocks could be 4.28 billion years old. It’s rare to find rocks that date back to when the Earth’s mantle was forming. It was quite a tumultuous time, and most rocks were smashed up into tiny pieces again and again. Learning more about these whole rocks could help us gain a better understanding of the very beginnings of our planet.
